IFNG and tuberculosis: However, how to control LTBI in intermediate-burden countries such as South Korea where the incidence rate of active TB is 80/100,000 [3] is not well understood, although WHO recommends the tuberculin skin test (TST) and interferon-gamma release assay (IGRA) guidelines based on TB burden with a cut-off level of 100/100,000 that discriminates the high from low burden in addition to economic status [4,5].